U.S. Pat. No. 4,724,458 granted Feb. 9, 1988 to Roy et al, shows a color reproduction apparatus in which consecutive electrostatically held toner images are superimposed at a transfer station. The electrostatically held images are carried on an endless belt. The transfer station includes a drum which carries a receiving sheet on its periphery with the intended receiving surface exposed. The drum is driven so that the receiving surface moves at the same speed as the belt by gearing between a sprocket driven by the belt and the drum.
When used to produce a high quality color image in which toners are combined to produce intermediate colors, the quality of the image is dependent upon the accuracy of registration of those images. Even very slight misregistration can change the perceived hue of the image as well as its sharpness. Because the web carries the images to be transferred consecutively and the web has the tendency to follow itself in the same path for at least three or four images, crosstrack registration is not generally a source of substantial misregistration. However, utilizing structure shown in FIG. 8 of the Roy patent, intrack registration is very much dependent upon the preciseness of the sprocket and gear train. That FIG. 8 structure shows a sprocket gear coaxial with and driven with the sprocket, and two intermediate gears transmitting the drive from the sprocket gear to a drum gear which is coaxial with and driven with the drum. Although that structure gives reasonably good results for most applications, even close attention to precision in the manufacture of the gearing does not yield the highest quality of registration.